The mouse has become the preferred species for genetic manipulation, but approaches for characterizing the mouse cardiac phenotype and performing physiologic studies on cardiovascular function on the intact mouse heart in vivo generally have lagged behind the rapid advances in transgenic and gene-deletion technologies. This mouse physiology core will improve and apply miniaturized hemodynamic and imaging techniques for physiological studies, in intact adult mice, as well as in intact mouse embryos. Also, techniques for studying isolated cardiomyocytes will be available, along with an approach for viral transfection of the heart. Microsurgical techniques also have been devised in mice to produce chronic pressure overload on either the left and right ventricle, as well as chronic volume overload. Miniaturized imaging techniques for the heart involve transthoracic ultrasound (2-D, M-mode and Doppler echocardiography) and x-ray microangiography for adult mouse hearts, and intravital videomicroscopy for embryonic mouse hearts. High- fidelity catheter tip micromanometry is now available for assessing intracardiac pressures and myocardial contractility in anesthetized open or closed-chest animals, as well as in the unanesthetized state.